1. Field of the Invention
The present invention relates to an apparatus for transmitting and receiving data in radio data communication. More specifically, the present invention relates to an apparatus compatible with a conventional wireless local area network communication system, for transmitting and receiving data in high-speed and a method thereof. In addition, the present invention relates to a wireless communication system for increasing data rates from 54 Mbps which has been a maximum data rate in the conventional wireless local area network communication system, to hundreds of Mbps.
2. Description of the Related Art
In the conventional IEEE 802.11a wireless local area network (LAN) system using an orthogonal frequency division multiplexing method, a 20 MHz bandwidth is divided into 64 subcarriers, and 52 subcarriers of the 64 subcarriers are used to transmit data and pilot symbols. That is, the data are transmitted at a maximum speed of 54 Mbps by using a single antenna and the 20 MHz bandwidth.
The present invention provides an apparatus for transmitting and receiving data while being compatible with the conventional IEEE 802.11a orthogonal frequency division multiplexing (OFDM) method. The apparatus uses multiple antennas and a plurality of 20 MHz bandwidths to achieve a high data rate.
In response to the demand for high-speed multimedia data transmission, various practical applications requesting more than 100 Mbps throughput have been being developed. However, even the wireless LAN system having the greatest throughput of the current wireless communication systems does not offer over 25 Mbps of throughputs. Therefore the present invention suggests a system offering a data rate which is four times as fast as the conventional IEEE 802.11a system, or more.
In detail, the present invention suggests a configuration in which a number of antennas and bandwidths are systematically controlled and a maximum data rate is controlled according to characteristics of a system. The present invention also suggests a method for providing compatibility with the conventional system.
FIG. 1 shows a block diagram for representing a system for transmitting and receiving data in the conventional wireless LAN.
In the conventional IEEE 802.11a system shown in FIG. 1, 20 MHz bandwidth is divided into 64 subcarriers. Among the 64 subcarriers, 48 subcarriers are used for data transmission 4 subcarriers are used for pilot symbol transmission, and a DC subcarrier and the other 11 subcarriers are not used.
A convolutional code having ½, ⅔, and ¾ code rates, binary phase shift keying (BPSK) modulation, quaternary phase shift keying (QPSK) modulation, 16 quadrature amplitude modulation (QAM) modulation, and 64 quadrature amplitude modulation (QAM) are used to transmit the data.
In the system shown in FIG. 1, when a source unit 101 generates binary data, the binary data are provided to a scrambler 102 for randomizing a permutation of the binary data.
A convolution encoder 103 performs channel encoding according to a code rate and a modulation determined by a desired data rate, and a mapper 105 performs modulation to map the previous data permutation on a complex symbol permutation.
An interleaver 104 provided between the convolution encoder 103 and the mapper 105 interleaves the data permutation according to a predetermined rule. The mapper 105 establishes the complex number permutation to be a group of 48, and a subcarrier allocator 107 forms 48 data components and 4 pilot components from pilot unit 106.
A 64 inverse fast Fourier transform (64-IFFT) unit 108 performs an inverse fast Fourier transform on the 48 data and 4 pilot components to form an OFDM symbol.
A cyclic prefix adder 109 adds a cyclic prefix which is a guard interval to the OFDM symbol.
A radio frequency (RF) transmit unit 110 transmits a transmission frame formed by the above configuration on a carrier frequency. An RF receive unit 112 receives the transmission signal (the transmission frame transmitted on the carrier frequency) through a radio channel 111. The radio channel 111 includes a multi-path fading channel and Gaussian noise added from a receive terminal.
The RF receive unit 112 of the receive terminal receives the distorted signal passing through the radio channel 111, and down-converts the signal transmitted on the carrier frequency to a base band signal in an opposite manner executed by the RF transmit unit 110 of the transmit terminal.
A cyclic prefix eliminator 113 eliminates the cyclic prefix added in a transmitter. A 64 fast Fourier transform (64-FFT) unit 114 converts a received OFDM symbol into a signal of a frequency domain by performing an FFT operation.
A subcarrier extractor 115 transmits the 48 complex symbols corresponding to the data subcarrier among 64 outputs to an equalizing and tracking unit 117, and transmits the 4 subcarriers corresponding to the pilot to an equalizing and tracking parameter estimator 116.
The equalizing and tracking parameter estimator 116 estimates a phase change caused by frequency and time errors by using the known symbols, and transmits an estimation result to the equalizing and tracking unit 117.
The equalizing and tracking unit 117 uses the above estimation result to perform a tracking operation. The equalizing and tracking unit 117 also performs a frequency domain channel equalization operation for equalizing channel distortion in the frequency domain in addition to the tracking process.
A demapper 118 performs a hard decision operation for converting the output complex number after the channel equalizing and tracking operation into the binary data, or performs a soft decision for converting the output complex number into a real number. A deinterleaver 119 deinterleaves the data in an inverse process of the interleaver 104, and a Viterbi decoder 120 performs decoding of the convolution code to correct errors and restore the transmitted data.
A descrambler 121 randomizes the data transmitted from the source unit in a like manner of the scrambler 102 and transmits the received data to a sink unit 122.
The conventional wireless LAN system shown in FIG. 1 has limits of data rate and throughput, and therefore the system is difficult to apply to a service requiring a high data rate such as a high quality moving picture service.
Systems using multiple bandwidths and antennas to provide a high speed data rate have previously not been compatible with the conventional transmitting and receiving system.
Accordingly, the present invention provides an apparatus for transmitting and receiving for providing compatibility with the conventional wireless communication system, and the high speed data rate and a method thereof.